Hydroxychloroquine: what it treats, how to take it, side effects
Last updated September 3, 2026.
Hydroxychloroquine is an antimalarial that also calms the immune system. You may know it as Plaquenil. It treats lupus and rheumatoid arthritis, and prevents and treats malaria - and it comes with a standing appointment you cannot skip: the eye exam.
What does it treat?
Discoid and systemic lupus erythematosus, rheumatoid arthritis, and the prevention and treatment of acute malaria attacks in adults and children weighing more than 31 kg (68 pounds). For lupus and arthritis, it works by decreasing immune-system activity.
How do you take it?
With food or milk, swallowed whole - never split, chewed, or crushed. For lupus or rheumatoid arthritis, it is usually once or twice a day, same times every day; improvement takes several weeks to months, and stopping brings the symptoms back. For malaria prevention, one dose once a week on exactly the same day each week, starting 1 to 2 weeks before travel and continuing 4 weeks after return. Take it exactly as directed, and never stop the lupus or arthritis course without your doctor. Missed dose: take it when you remember unless the next one is close; never double up. If you take antacids, space them 4 hours before or 4 hours after this one.
Side effects to know
- Common: headache, loss of appetite, nausea, diarrhea, stomach pain, vomiting, difficulty hearing or ringing in the ears, hair loss, and hair color changes.
- Serious - call your doctor immediately: allergic reactions (hives, rash, facial or throat swelling, trouble breathing or swallowing); blisters on the skin, eyes, lips, or in the mouth; muscle weakness; burning, numbness, or tingling in the hands or feet; the liver cluster (extreme tiredness, yellowing skin or eyes, dark urine, upper right stomach pain); unusual bleeding or bruising; infection signs; mood or mental changes; fast or irregular heartbeat; and lightheadedness, dizziness, or fainting.
Who should not take it?
The eye risk is the famous one: hydroxychloroquine can cause serious and potentially irreversible eye problems, so regular eye exams are part of the prescription - and blurred vision, floaters, flashes of light, or any vision change gets reported. Flag a personal or family history of prolonged QT interval, heart failure, heart attack, irregular heartbeat, low magnesium or potassium, psoriasis, porphyria, G6PD deficiency or other blood disorders, seizures, existing vision problems like macular degeneration, diabetes, kidney or liver problems, and heavy alcohol use. It can cause low blood sugar - know the symptoms (dizziness, sweating, confusion, fainting). Cimetidine interacts. The label also notes rare reports of suicidal behavior. If you become pregnant, call your doctor.
When is it an emergency?
Trouble breathing or swallowing, fainting, or a fast or irregular heartbeat is a 911 call. So is a severe low-blood-sugar episode. Mood or mental changes on this drug are a same-day call to your doctor - and if thoughts of harming yourself ever appear, the 988 Suicide and Crisis Lifeline (call or text 988) is there anytime. For an overdose, call Poison Control at 1-800-222-1222. Pymander's escalation routing is built and tested specifically for this class of decision; see the safety architecture working paper.
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Common questions
Why do I need eye exams on hydroxychloroquine?
Because the retina is the vulnerable spot. MedlinePlus says hydroxychloroquine may cause serious and potentially irreversible eye problems, and that you will probably need regular eye exams during treatment. The exams catch early changes while they are still reversible - and between exams, blurred vision, floaters, or flashes of light are a call-your-doctor symptom, not a wait-for-the-appointment one.
Why do I take hydroxychloroquine with food or milk?
Tolerance and consistency. MedlinePlus directs the tablets be taken with food or milk - it softens the stomach upset, which is one of the most common effects, and anchors the dose to a routine you already keep. Swallow them whole; never split, chew, or crush.
Can I take antacids with hydroxychloroquine?
Yes, with a 4-hour buffer. MedlinePlus says to take antacids 4 hours before or 4 hours after hydroxychloroquine - they block its absorption if they arrive together. Same caution for cimetidine, the OTC heartburn drug: flag it before starting, per MedlinePlus.
How long does hydroxychloroquine take to work for lupus or arthritis?
Weeks to months. MedlinePlus says rheumatoid arthritis symptoms should improve within several weeks to months - this is a slow-acting, stay-the-course drug, and stopping it brings the symptoms back. Judge it at the three-month mark with your doctor, not week by week.
Can I drink alcohol while taking hydroxychloroquine?
Flag it first. MedlinePlus lists drinking large amounts of alcohol among the things your doctor must know before you start - the drug is processed by the liver, and heavy drinking changes the risk. The explicit rule for your situation comes from your doctor.
Does hydroxychloroquine affect mood?
It can. Mood or mental changes are on MedlinePlus's call-your-doctor-immediately list, and the label notes rare reports of suicidal behavior. Most people never see this, but a mood shift on this drug is a medication question - report it early. And 988 (call or text) is there anytime you need it.